nikomatsakis

The "Hashtable Problem"

There is a danger with typeclasses only on functions because they permit a lack of coherence. This danger is particularly acute with collections, where the definition of a particular interface---such as hashable or ord---may be used in structuring the data structure. This renders the data structure corrupt when used with a different implementation.

To see the problem, consider a hashtable defined something like this:

fperez

#!/usr/bin/env python
"""
Interactive execution with automatic history, tries to mimic Mathematica's
prompt system. This environment's main features are:

- Numbered prompts (In/Out) similar to Mathematica. Only actions that produce
  output (NOT assingments, for example) affect the counter and cache.

- The following GLOBAL variables always exist (so don't overwrite them!):
  _p: stores previous result which generated printable output.

vsergeev

Busybox "Embedded Linux from Scratch" Distribution for the Beaglebone

Prepare your Build Sandbox

$ mkdir -p beaglelfs/{sources,rootfs_install,boot_mnt,rootfs_mnt}

Acquire an ARM Toolchain

Download the latest i686 Binary TAR of the ARM GNU/Linux (glibc-based) Lite Toolchain:

jboner

Latency Comparison Numbers (~2012)
----------------------------------
L1 cache reference                           0.5 ns
Branch mispredict                            5   ns
L2 cache reference                           7   ns                      14x L1 cache
Mutex lock/unlock                           25   ns
Main memory reference                      100   ns                      20x L2 cache, 200x L1 cache
Compress 1K bytes with Zippy             3,000   ns        3 us
Send 1K bytes over 1 Gbps network       10,000   ns       10 us
Read 4K randomly from SSD*             150,000   ns      150 us          ~1GB/sec SSD

hellerbarde

Latency numbers every programmer should know

L1 cache reference ......................... 0.5 ns
Branch mispredict ............................ 5 ns
L2 cache reference ........................... 7 ns
Mutex lock/unlock ........................... 25 ns
Main memory reference ...................... 100 ns             
Compress 1K bytes with Zippy ............. 3,000 ns  =   3 µs
Send 2K bytes over 1 Gbps network ....... 20,000 ns  =  20 µs
SSD random read ........................ 150,000 ns  = 150 µs

Read 1 MB sequentially from memory ..... 250,000 ns = 250 µs

paulp

Hello scala, my old friend
I've come to take you home again
Because a feature slowly creeping
left me plagued with doubts and weeping
and the version that was tagged in the repo
just has to go
it lacks the signs of soundness

On sleepless nights I hacked alone
applying ant and other tools of stone

mattetti

package main

import (
	"bytes"
	"fmt"
	"io"
	"log"
	"mime/multipart"
	"net/http"
	"os"

danbe

# -*- coding: utf-8 -*-
from collections import namedtuple
import json
import urllib.parse
#import telnetlib
import time
import os.path
import filecmp
import random
import string

shamil

How to mount a qcow2 disk image

This is a quick guide to mounting a qcow2 disk images on your host server. This is useful to reset passwords, edit files, or recover something without the virtual machine running.

Step 1 - Enable NBD on the Host

modprobe nbd max_part=8

Airblader

#!/usr/bin/env python2.7
# -*- coding: utf-8 -*-
# vim:ts=2:sw=2:expandtab

import os
import xcb
from xcb.xproto import *
from PIL import Image

XCB_MAP_STATE_VIEWABLE = 2